The question's been around forever -- and so have the myths surrounding it.

Many factors influence how your child turns out; don't attribute large effects to a subtle factor such as birth order.

But the debate over the impact of birth order gained new urgency this summer when the results of a new study were announced: Firstborns' IQs tend to be higher than those of their younger siblings.

Does that mean later-born kids are destined to be less accomplished and successful? Studies like this don't tell the whole story -- and neither do birth-order stereotypes. Here's how to bring out the best in each child:

What the latest study found

Norwegian scientists analyzed test results and birth data from more than 241,000 military conscripts and found that oldest children had an average IQ of 103, second children came in at 101, and third-borns were at 100.

Is that a big spread? It's not a difference you'd ever notice, but some researchers say it could mean the difference between getting into a top college versus a second-tier one.

What accounts for the difference? Nobody knows. There's speculation that eldest kids benefit from having their parents' undivided attention for a while -- until another swaddled bundle arrives home from the hospital, that is. Or it could be that moms and dads have especially big dreams for their first kid, and the child picks up on it. Another theory: Eldest children are given more responsibility and are expected to show their sibs the ropes, which builds brainpower. Parenting.com: The kid gap

Will this scenario play out in your family? Not so fast. Like all studies, this one has limitations:

• The study's Norwegian -- maybe there's something special in the lingonberries over there.

• The subjects were all male -- who knows if it's true for sisters?

• IQ numbers themselves aren't rock-solid. "Today's tests have a surprising degree of error," says Nathan Haselbauer, founder and president of the International High IQ Society. A score of 110, he says, means that your true score is probably between 105 and 115. And older IQ tests were even less precise than modern ones. "Since the Norwegian study used data as old as 1967, I'd say that trying to find meaning in the three-point gap it found could be nothing more than a wild goose chase," Haselbauer says.

• While small differences like the ones this study found are important spread across the entire population, they're likely next to meaningless within a family. Remember that the averages for everyone in this study -- firstborn and last -- were well within the normal range.

Seeing past stereotypes

Does birth order affect children in other ways, shaping personalities, interests, and futures? Some experts believe it does, and in some cases there's intriguing, though inconclusive, evidence. But many factors, from genes to life in the womb, influence how your child turns out, so it's a mistake to attribute large effects to a subtle factor like the order in which your child was born. Here's what you may have heard, and how to use the information to your advantage. Parenting.com: How to treat your children fairly

Firstborns

Eldest children, it's commonly claimed, are natural leaders and problem solvers, with strong organizational and reasoning skills. There's no study comparable to the Norwegian one to back this up, but it's gained a lot of currency because it has the appearance of logic. Twenty-one of the first twenty-three American astronauts were firstborns, and they're well represented among Rhodes scholars and university professors, says Kevin Leman, Ph.D., author of "The Birth Order Book: Why You Are the Way You Are."

Firstborns are also sometimes said to be better at relating to adults than to other kids, since they're so used to interacting with their parents.

What to do: Nothing. The best advice -- for parenting any child -- is not to let any theories pigeonhole your child's personality. You need to help him be the best version of who he naturally is, not what you might have read he should be.

That said, older kids often do have a lot of responsibility thrown at them ("Get your brother for me, would you?" "Can you help your sister with her socks?"). So remember to ease up sometimes, and don't expect your firstborn to be a third parent to his younger sibs -- a huge responsibility for any young child. And when he misbehaves, give him consequences but spare him the "you need to set an example for your little sister" speech. No one needs a guilt trip like that. Parenting.com: Guide to siblings

Middle children

Middle kids are said to be great negotiators and peacemakers, with laid-back attitudes and a love of socializing. As such, they're thought to be natural schmoozers and consensus builders when they grow up. According to Linda Dunlap, Ph.D., a birth-order--theory expert and professor of psychology at Marist College in Poughkeepsie, New York, they're the most likely to move far from home once they grow up, partly because they're seeking a clear identity after having spent their early years sandwiched between sibs.

Some middle kids suffer from the firstborn's long shadow, and because of it, it's said, are prone to rebelliousness and competitiveness.

What to do: Go out of your way to make your middle child feel noticed. Display as many pictures of her as you do of your first and hang her artwork on the fridge just as often. Ask her what she thinks about that book you just read or the newest Webkinz -- then listen to her opinions. And give her some of the responsibilities you usually automatically give to her older sib, says Thomas Connellan, Ph.D., author of "Bringing Out the Best in Others: 3 Keys for Business Leaders, Educators, Coaches and Parents." Let her be the one to hold the money for the movie tickets for a change. Parenting.com: Is one child enough?

Last children

Last-borns have the most experienced parents, of course. But how does it affect them? Leman and Connellan (as well as a host of nonexperts) say they're the least likely to be disciplined, perhaps because Mom and Dad are by then too laid-back --or worn down -- to freak over every infraction. Popular wisdom also has it that youngest kids are doted on, and because of it become adept at wrapping people around their little fingers and clowning to get attention.

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There are drawbacks to being perceived as a loosely supervised charmer, however. Youngest children may suffer from other people's assumptions that they are spoiled, stubborn, and manipulative.

What to do: Although your youngest's antics may seem especially cute, since she's so adorably little compared with her bigger sibs, she needs limits as much as they do. Hold her responsible for her actions, whether it's making sure she cleans up her toys or says "sorry" when she's been fresh to a friend. Make sure she gets her share of chores, as well as her chance to occasionally choose which movie the family watches or what dessert you'll serve. Most important: Whether she was born first or last, just let her be herself.